San Francisco Airport: Sinking Or Stable?

San Francisco International Airport (SFO) is one of the busiest airports in the US, but it has a problem. The airport is sinking into the mud at a rate of about 10 millimetres (0.4 inches) per year, according to new satellite data. This subsidence is caused by the compaction of man-made landfill and soft bay mud, and it's putting the airport at risk of damage and natural disasters. With rising sea levels due to global warming, there are concerns about the airport's future.

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San Francisco Airport is sinking by 10mm annually

San Francisco International Airport is slowly sinking into the mud at an average rate of about 10 millimeters (0.4 inches) per year. This subsidence is due to the compaction of man-made landfill and soft bay mud on which the airport is built. While the rate of sinking may sound negligible, it poses a serious hazard to the millions of travelers who fly every day. Differential sinking along a runway increases the risk of damage, increases maintenance costs, and puts users at risk. Even a minute crack in a runway caused by subsidence would render the entire runway unusable.

The subsidence was detected by researchers at Virginia Tech using radar on European Space Agency Sentinel-1 satellites and advanced data processing techniques. They measured 15 coastal airports over seven years, from 2015 to 2022, and found that San Francisco International Airport had the fastest subsidence rate of all the airports studied. Los Angeles International Airport (LAX), in comparison, had the slowest rate of subsidence.

The sinking of San Francisco International Airport is not an isolated incident. Large portions of San Francisco's Mission Bay and the city's luxury skyscraper Millennium Tower, also known as the Leaning Tower of San Francisco, are also showing signs of subsidence. Additionally, the sea level around the Bay is rising due to global warming, which could make the airport more prone to natural disasters.

To address the issue of subsidence, the Virginia Tech team recommended continuous monitoring to quickly fix any problems that arise. They also suggested that engineering solutions can be deployed, but more data is needed to prioritize which sections of the runways require attention.

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This is due to the compaction of man-made landfill and soft bay mud

San Francisco International Airport is subsiding at a rate of about 10 millimetres, or 0.4 inches, per year. This is due to the compaction of man-made landfill and soft bay mud, on which the airport is built. The subsidence is unevenly distributed across the airport, which could lead to cracks in the runways. The compaction of landfill and mud also affects other areas in San Francisco, such as the luxury skyscraper Millennium Tower and large portions of San Francisco's Mission Bay.

The compaction of man-made landfill and soft bay mud is a result of various factors, including the weight of the structures built on them and the natural settlement of the landfill over time. The landfill used for the airport construction was likely intended to provide a stable base for the runways and buildings. However, as the landfill compacts, it can no longer support the weight adequately, leading to subsidence.

Additionally, the soft bay mud underlying the landfill layer is also susceptible to compaction. Bay mud is a soft, organic-rich sediment that is highly compressible. As the weight of the landfill and structures above increases, the bay mud compresses and consolidates, contributing to the overall subsidence of the airport.

The effects of subsidence are not limited to the airport itself. The surrounding area, including nearby buildings and infrastructure, can also be impacted. As the land sinks, the foundations of nearby structures may settle unevenly, leading to cracks and other structural issues. This could affect roads, bridges, and other critical infrastructure in the vicinity of the airport.

To address the issue of subsidence, continuous monitoring is essential. By regularly measuring elevation changes and analysing data, engineers can identify areas of concern and prioritise sections of the runways that require reinforcement or repair. Additionally, implementing engineering solutions, such as improved foundation designs or ground improvement techniques, can help mitigate the effects of compaction and reduce the rate of subsidence.

Rising sea levels caused by global warming pose further risks

San Francisco International Airport, built on soft bay mud, is slowly sinking into the ground. The subsidence is uneven across the airport, and runways are sinking at a rate of about 10 mm (0.4 inches) per year. While this may seem insignificant, it could cause cracks in the runways, rendering them unusable. This subsidence, coupled with rising sea levels, could make the airport more vulnerable to natural disasters.

The consequences of rising sea levels are far-reaching. In the San Francisco Bay area, saltwater intrusion from the rising sea levels can contaminate freshwater aquifers, impacting water supplies and natural ecosystems. Additionally, the loss of coastlines, territorial disputes, resource scarcity, and mass displacement of people can lead to deepening tensions and legal complexities. The impact on food security is also significant, as much of the world's agriculture is concentrated on coastal plains and low-lying islands.

The rising sea levels also pose risks to critical infrastructure, such as airports, roads, and bridges. The San Francisco International Airport, being a coastal airport, is particularly vulnerable to the effects of rising sea levels and subsidence. The combination of sinking land and rising waters could increase the airport's susceptibility to natural disasters, such as floods or storms. Additionally, the maintenance costs associated with addressing the subsidence and protecting against rising sea levels can be substantial, placing a strain on limited infrastructure funds.

To mitigate these risks, continuous monitoring and engineering solutions are necessary. More data can help prioritize sections of the runways that require urgent attention and inform decision-making for adapting to rising sea levels. Addressing the root cause of climate change by reducing greenhouse gas emissions is also crucial to prevent irreversible catastrophes and limit the magnitude of sea-level rise.

The subsidence could crack runways and damage infrastructure

San Francisco International Airport (SFO) is slowly sinking into the mud at a rate of about 10 millimetres (0.4 inches) per year, according to new satellite data. This is due to the compaction of man-made landfill and soft bay mud on which the airport was built. While this measurement is tiny, there are concerns that the subsidence, which is experienced unevenly across the airport, could crack the runways.

Oluwaseyi Dasho, an environmental hazard specialist at Virginia Tech, said:

> Differential sinking along a runway increases the risk of the runway getting damaged, increases the cost of maintenance, and increases the risk to users. Even though it’s just a minute portion of the runway, if it causes a crack, that would render the whole runway unusable.

The subsidence, coupled with rising water levels around the Bay due to global warming, could also make the airport more prone to natural disasters. Dasho and his advisor, Manoochehr Shirzaei, a geophysicist at Virginia Tech, wanted to better understand how coastal airports' runways, roads, and other transportation infrastructure are faring. Shirzaei said:

> Some engineering solutions can be deployed. But we need to know where to start. More data will help prioritize the sections of the runways that need attention.

The Virginia Tech team recommended continuous monitoring so that problems can be quickly fixed.

Coastal airports in the US are at risk due to climate change and a lack of funds

Coastal airports in the United States are at risk due to climate change and a lack of funds. San Francisco International Airport (SFO) is a prime example of this, as it is one of the fastest-sinking airports in the nation, with subsidence rates of up to 10 millimeters (0.4 inches) per year. This is due to the compaction of man-made landfill and soft bay mud on which the airport is built, as well as rising sea levels caused by global warming. The combination of subsidence and rising water levels increases the airport's vulnerability to natural disasters and flooding.

The problem is not unique to San Francisco. A study by Virginia Tech researchers found subsidence at 15 coastal airports across the United States, with Los Angeles International Airport (LAX) experiencing the slowest rate of subsidence. The varying rates of subsidence are attributed to the different materials used in airport construction and the surrounding geological conditions.

Climate change poses a significant threat to coastal airports, with rising sea levels, storm surges, and extreme weather events increasing the risk of flooding and disrupting airport operations. Heatwaves can also impact airports, affecting plane capacity and restricting take-off, as hotter temperatures make it more difficult for airplanes to gain enough lift. Additionally, extreme weather events can ground planes and disrupt air travel, with weather currently causing more than 75% of air traffic delays in the United States.

The lack of federal programs and funding dedicated to building resilience at commercial service airports further exacerbates the problem. Oluwaseyi Dasho, an environmental hazard specialist at Virginia Tech, noted that "the funding to maintain airport infrastructures is quite limited, so many are getting dilapidated." The demand for maintenance and updates far exceeds the budget allocated in the infrastructure bill. This lack of funding puts coastal airports, which are critical to the national economy, at even greater risk.

To address these challenges, airports must develop adaptive strategies and integrate climate change risks into their training programs, communications protocols, and capital planning. Additionally, federal and local leaders need to prioritize protecting these economic assets by incentivizing airport authorities to develop resilience plans and providing support for necessary updates and adaptations.

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